Methods and apparatus for detecting a potential fault in a positioning device

ABSTRACT

Methods and apparatus for detecting a potential fault in a positioning device, the apparatus including at least one memory for storing instructions, and at least one controller configured to execute the instructions to perform operations including obtaining information about a received signal received by the positioning device, the information including at least one of a control parameter or an estimation of bias based on the received signal; determining whether the potential fault is detected, based on the information and a detection threshold; and in response to a determination that the potential fault is detected, generating an indication that the potential fault is detected.

TECHNICAL FIELD

The present disclosure relates to fault detection for a positioningdevice, and more particularly, to methods and apparatus for detecting apotential fault in a positioning device.

BACKGROUND

Monitoring conditions of a receiver and a received signal for apositioning device enable providing accurate and reliable positioninformation. External components and circuits of the receiver areexpected to operate without a fault to support operations of thereceiver in the positioning device. A catastrophic failure of anexternal circuit or component may be easily detected as a loss of thesignal received by the receiver. However, the failure needs not becatastrophic. Even partial failure of components may be problematic andsuch partial failures in practice are difficult to detect. For instance,a fault may arise in any component connected to the receiver. Forexample, a fault may occur in a component of an impedance matchingnetwork. Alternatively, a component in a functional block, for example asurface acoustic wave (SAW) filter, may experience a fault, e.g., due tovibration, which may cause a distortion of the received signal by thereceiver, but this signal may still potentially be processed and trackedby the receiver. Additionally, the receiver may still be able to receivenew signals through the faulted SAW filter and attempt to compute aposition based on the distorted signal received by the receiver.Nonetheless, the fault of the SAW filter on a radio frequency (RF) pathmay cause poor group delay characteristics of the newly receivedsignals, which can cause severe changes in measurements and result inposition errors. The position errors may cause non-compliance with arequirement for functional safety in some applications. For example, infunctionally safe systems, a reported position of a positioning systemshould be trustworthy. The failure of components as described abovewould cause the reported position to be untrustworthy, and hence need tobe detected and reported.

SUMMARY

Embodiments of the present application provide improved methods andapparatus for detecting a potential fault in a positioning device.

These embodiments include an apparatus for detecting a potential faultin a positioning device. The apparatus includes at least one memory forstoring instructions, and at least one controller configured to executethe instructions to perform operations including obtaining informationabout a received signal received by the positioning device, theinformation comprising at least one of a control parameter or anestimation of bias based on the received signal; determining whether thepotential fault is detected, based on the information and a detectionthreshold; and in response to a determination that the potential faultis detected, generating an indication that the potential fault isdetected.

These embodiments also include a method for detecting a potential faultin a positioning device. The method includes obtaining information abouta received signal received by the positioning device, the informationcomprising at least one of a control parameter or an estimation of biasbased on the received signal in the positioning device; determiningwhether the potential fault is detected, based on the information and adetection threshold; and in response to a determination that thepotential fault is detected, generating an indication that the potentialfault is detected.

These embodiments further include a non-transitory computer-readablemedium for storing instructions which, when executed, cause a controllerto perform operations for detecting a potential fault in a positioningdevice. The operations including obtaining information about a receivedsignal received by the positioning device, the information comprising atleast one of a control parameter or an estimation of bias based on thereceived signal; determining whether the potential fault is detected,based on the information and a detection threshold; and in response to adetermination that the potential fault is detected, generating anindication that the potential fault is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary fault detector and anexemplary receiver of a positioning device, consistent with embodimentsof the present disclosure.

FIG. 2 is a flow chart of an exemplary method for detecting a potentialfault in a positioning device, consistent with embodiments of thepresent disclosure.

FIG. 3 is a block diagram of an exemplary front-end circuit in areceiver of a positioning device, consistent with embodiments of thepresent disclosure.

FIG. 4 is a block diagram of an exemplary positioning device, consistentwith embodiments of the present disclosure.

FIG. 5 is a block diagram of an exemplary antenna subsystem of apositioning device, consistent with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which similar numbersin different drawings represent the same or similar elements unlessotherwise represented. The implementations set forth in the followingdescription of exemplary embodiments do not represent allimplementations consistent with the invention. Instead, they are merelyexamples of apparatuses and methods consistent with aspects related tothe invention as recited in the appended claims.

A positioning device usually requires signals from four or moresatellites in a positioning system to determine a position. Forconvenience of description, the positioning device is described hereinas receiving a signal from the positioning system to determine theposition.

FIG. 1 is a block diagram of an exemplary fault detector 140 and anexemplary receiver 120 of a positioning device 160, consistent withembodiments of the present disclosure. As shown in FIG. 1, positioningdevice 160 includes receiver 120 and fault detector 140. Receiver 120includes a front end 121, an automatic gain controller (AGC) 122, adigital processing circuit 124, a tracking engine 126, and a navigationengine 128. Fault detector 140 includes a controller 142 and a memory144. One or more of these elements in FIG. 1 may be included fordetecting a potential fault in positioning device 160. These elementsmay be configured to transfer data and send or receive instructionsbetween or among each other.

In receiver 120, front end 121, digital processing circuit 124, trackingengine 126, and navigation engine 128 are coupled in cascade to receivea signal via an input 101, determine position and navigation informationbased on the received signal, and output navigation information via anoutput 103 to, for example, a user, a navigation user interface, anavigation device, or a server. AGC 122 is coupled to front end 121 tomeasure signal strength and control amplification gain of a programmablegain amplifier (PGA) in front end 121.

AGC 122 is configured to control a received signal strength at an inputof digital processing circuit 124 such that a required signal-to-noiseratio (SNR) for proper analogue-to-digital conversion and digitalprocessing is met. For example, if the received signal strength is weak,AGC 122 is configured to boost a gain for the received signal in orderto minimize noise and bring a signal level of the received signal to anacceptable SNR. If the received signal strength is strong, e.g., becauseof the presence of interference, AGC 122 is configured to attenuate thegain for the received signal in order to avoid signal clipping andnonlinear distortion that may deteriorate the SNR of the receivedsignal.

Digital processing circuit 124 is configured to receive and process areceived digital signal. In some embodiments, digital processing circuit124 includes a processor configured to execute instructions stored in amemory to receive and process the received digital signal. Digitalprocessing circuit 124 is configured to filter, demodulate, and decodethe received digital signal to obtain information transmitted from oneor more satellites and send the information to tracking engine 126.

Tracking engine 126 is configured to track and decode received signalsand perform pseudorange and phase measurements. In some embodiments,tracking engine 126 includes a processor configured to executeinstructions stored in a memory to track and decode the received signalsand perform the measurements.

Navigation engine 128 is configured to determine a position based ontracked signals, decoded information, and/or measurements from trackingengine 126. In some embodiments, navigation engine 128 includes aprocessor configured to execute instructions stored in a memory todetermine a position based on the tracked signals, decoded information,and/or measurements. Navigation engine 128 is configured to outputposition information via output 103.

In some embodiments, digital processing circuit 124, tracking engine126, and/or navigation engine 128 may be the same circuit or processorand memory configured to perform operations as described with referenceto FIG. 1. For example, a processor and a memory can be configured toperform the described operations of digital processing circuit 124,tracking engine 126, and navigation engine 128. As another example,digital processing circuit 124 includes digital circuits for digitalsignal processing, and a processor and a memory are configured toperform the described operations of tracking engine 126 and navigationengine 128.

In fault detector 140, controller 142 is coupled to memory 144.Controller 142 includes any appropriate type of general-purpose orspecial-purpose microprocessor, digital signal processor, ormicrocontroller. After fault detector 140 determines whether a potentialfault is detected in positioning device 160, fault detector 140 isconfigured to generate an indication signal 104 that indicates whetheror not the potential fault is detected. For example, when a potentialfault is detected, indication signal 104 may output a logic “one” orhigh-voltage level. Conversely, if fault detector 140 does not detect apotential fault, indication signal 104 may output a logic “zero” orlow-voltage level for instance. Controller 142 can be representative ofone or more processors and/or controllers in fault detector 140.

Memory 144 may include any appropriate type of mass storage provided tostore any type of information that controller 142 may need in order tooperate. Memory 144 may be a volatile or non-volatile, magnetic,semiconductor, optical, removable, non-removable, or other type ofstorage device or tangible (i.e., non-transitory) computer-readablemedium including, but not limited to, a read-only memory (ROM), a flashmemory, a dynamic random-access memory (RAM), and a static RAM. Memory142 may be configured to store one or more programs for execution bycontroller 142 for detecting a potential fault in positioning device160, as disclosed herein.

Memory 144 may be further configured to store information and data usedby controller 142. For instance, memory 144 may be configured to storegain values, biases, and thresholds for detecting a potential fault inpositioning device 160.

In some embodiments, controller 142 and memory 144 of fault detector 140may be the same circuits, processor, and/or memory of receiver 120,configured to perform operations for detecting a potential fault inpositioning device 160, as disclosed herein.

As shown in FIG. 1, fault detector 140 is configured to receive aprogrammable gain amplifier (PGA) gain value from AGC 122 of receiver120 via a connection 121. In some embodiments, controller 142 isconfigured to execute instructions stored in memory 144 to detect apotential fault in positioning device 160 based on the PGA gain, asdisclosed herein. Alternatively, fault detector 140 is configured toreceive an inter-channel bias, an inter-system bias, and/or aninter-band bias from navigation engine 128 of receiver 120 via aconnection 123 from navigation engine 128. Controller 142 is configuredto execute instructions stored in memory 144 to detect a potential faultin positioning device 160 based on the inter-channel bias, inter-systembias, and/or inter-band bias, as disclosed herein.

In some embodiments, fault detector 140 includes one or more circuits toimplement fault detection methods disclosed herein by one or more finitestate machines.

FIG. 2 is a flow chart of an exemplary method 200 for detecting apotential fault in a positioning device, such as positioning device 160,consistent with embodiments of the present disclosure. Method 200 may bepracticed by fault detector 140 disclosed and illustrated in the presentdisclosure. For example, controller 142 is configured to executeinstructions stored in memory 144 to perform operations of method 200.As another example, fault detector 140 may include a control circuitconfigured to perform the operations of method 200 according to a finitestate machine. Method 200 includes obtaining information about areceived signal received by a positioning device (step 220), determiningwhether a potential fault is detected, based on the information and adetection threshold (step 240), and generating an indication that thepotential fault is detected in response to a determination that thepotential fault is detected (step 260).

Step 220 includes obtaining information about a received signal receivedby a positioning device. The information includes at least one of acontrol parameter or an estimation of bias based on the received signal.For example, as shown in FIG. 1, fault detector 140 is configured toreceive via connection 121 information about the PGA gain from AGC 122of receiver 120. The PGA gain is a gain control parameter that AGC 122determines based on signal strength of a received signal received bypositioning device 160. AGC 122 is configured to determine the PGA gainand send the PGA gain to a PGA in positioning device 160 to control again of the PGA for the received signal.

As another example, fault detector 140 is configured to receive viaconnection 123 information about an inter-channel bias, an inter-systembias, and/or an inter-band bias from navigation engine 128 of receiver120. The inter-channel bias, inter-system bias, and/or inter-band biasare estimations of biases that receiver 120 estimates based on thereceived signal received by positioning device 160.

Alternatively, fault detector 140 may be configured to receive both theinformation about the PGA gain and the information about theinter-channel bias, inter-system bias, and/or inter-band bias fordetecting a potential fault in positioning device 160, as describedbelow.

Step 240 includes determining whether a potential fault is detected,based on the information and a detection threshold. For example, faultdetector 140 is configured to determine whether a potential fault isdetected, based on the information about the PGA gain and a gainthreshold by the following steps. Fault detector 140 is configured tocompare the PGA gain with the gain threshold. In response to acomparison result that the PGA gain is greater than the gain threshold,fault detector 140 is configured to determine that the potential faultis detected in positioning device 160.

Alternatively, fault detector 140 can be configured to determine whethera potential fault is detected, based on the information about theinter-channel bias, inter-system bias, and/or inter-band bias, upperbias thresholds, and lower bias thresholds by the following steps. Faultdetector 140 is configured to compare one of the biases with at leastone of the corresponding upper or lower bias threshold. In response to acomparison result that the one of the biases is greater than thecorresponding upper bias threshold or less than the corresponding lowerbias threshold, fault detector 140 is configured to determine that thepotential fault is detected in positioning device 160.

In some embodiments, fault detector 140 can be configured to comparemultiple biases with corresponding upper or lower bias thresholds. Inresponse to a comparison result that one or more of the multiple biasesare greater than the corresponding upper bias thresholds or less thanthe corresponding lower bias thresholds, fault detector 140 isconfigured to determine that the potential fault is detected inpositioning device 160.

Moreover, in some embodiments, fault detector 140 can be configured todetermine whether a potential fault is detected, based on both theinformation about the PGA gain and the information about theinter-channel bias, inter-system bias, and/or inter-band bias, the gainthreshold, the upper bias thresholds, and the lower bias thresholds, asdescribed for embodiments herein.

Step 260 includes generating an indication that the potential fault isdetected in response to a determination that the potential fault isdetected. For example, when fault detector 140 determines that thepotential fault is detected, fault detector 140 is configured togenerate indication signal 104 to indicate whether the potential faultis detected in positioning device 160. Indication signal 104 can be analert signal of the potential fault in positioning device 160. The alertsignal may be used to indicate reliability of current positioningresults of positioning device 160. For example, when indication signal104 is a logic “one,” the current positioning results may be consideredunreliable. When indication signal 104 is a logic “zero,” the currentpositioning results may be considered reliable. In some embodiments,indication signal 104 can be used to decide whether navigationinformation should be updated according to the current positioningresults.

FIG. 3 is a block diagram of an exemplary front-end circuit 300 in areceiver of a positioning device, consistent with embodiments of thepresent disclosure. As shown in FIG. 3, front-end circuit 300 includes alow-noise amplifier (LNA) 320, a mixer 330, a local oscillator 331, alow-pass filter (LPF) 340, a PGA 360, and an analogue-to-digitalconverter (ADC) 380. LNA 320, mixer 330, LPF 340, PGA 360, and ADC 380are coupled in cascade to process a received signal from an input 301and output a received digital signal at an output 303. Mixer 330 iscoupled to local oscillator 331 to receive a local oscillator signal andmix the received signal with the local oscillator signal. An automaticgain controller (AGC), not shown in FIG. 3, is coupled to output 303 tomeasure received signal strength and send a gain control parameter via afeedback connection 355 to PGA 360.

LNA 320, mixer 330, LPF 340, and PGA 360 are configured to amplify andfilter the received signal from input 301. ADC 380 is configured toconvert the amplified and filtered the received signal into the receiveddigital signal. The AGC is configured to determine a suitable gain forsubsequently received signals based on a current received digitalsignal, and send the suitable gain as a gain control parameter viafeedback connection 355 to PGA 360. PGA 360 is configured to receive thegain control parameter and amplify or attenuate subsequently receivedsignals for a suitable SNR based on the gain control parameter from theAGC.

Front-end circuit 300 can operate as front end 121 in FIG. 1. In thisway, AGC 122 of FIG. 1 is configured to determine the suitable gain andsend the suitable gain as the gain control parameter via feedbackconnection 355 to PGA 360 in FIG. 3. Thus, front-end circuit 300 isdescribed below as an implementation of front end 121, where AGC 122 isconfigured to control a gain value of PGA 360.

When positioning device 160 starts to receive signals for positioning,AGC 122 is configured to adjust the gain of PGA 360 to a suitable valueof gain according to signal strength of initially received signals. Thereceived signals may have varied signal strengths due to interferenceand/or noise. Nonetheless, when all components of positioning device 160operate without a fault, the gain of PGA 360 may move up and down butremain within a gain threshold.

When a fault exists in one of the components of positioning device 160,the fault may cause anomalous degradation in the signal strength of thereceived signals. When the signal strength of the received signalsdegrades, AGC 122 is configured to increase the gain of PGA 360 in orderto maintain stable signal strength of the received signals, which mayresult in a considerable increase in the gain of PGA 360. The increasedgain of PGA 360 may be greater than the gain threshold because of thefault in the one of the components of positioning device 160.Accordingly, method 200 can be practiced by fault detector 140 fordetecting a potential fault in one of the components of positioningdevice 160 as described below.

The information about a received signal at step 220 includes informationabout a gain control parameter. The gain control parameter is, forexample, a current gain G_(c) of PGA 360 that AGC 122 sets to maintainsuitable signal strength of the received signals. PGA 360 has a nominalgain G_(N) after positioning device 160 is initialized and starts toreceive signals for positioning. The nominal gain G_(N) of PGA 360 is again that supports receiver 120 to receive signals with suitable signalstrength for processing. The nominal gain G_(N) can be an average gainthat supports positioning device 160 to operate and provide accurateposition fixes when all components of positioning device 160 operatewithout a fault.

The detection threshold in step 240 includes a gain threshold equal tothe nominal gain G_(N) plus a delta value of gain dG, i.e., the gainthreshold=G_(N)+dG. The delta value of gain dG can be, for example, 3 or5 dB, which is a margin to allow variations in the gain of PGA 360because of interference and/or noise.

Determining whether the potential fault is detected at step 240 includesdetermining whether the current gain Goof PGA 360 is greater than thegain threshold. Mathematically, this can be expressed as:

$\begin{matrix}{{{Potential}\mspace{14mu}{Fault}} = \left\{ \begin{matrix}{{Not}\mspace{14mu}{Detected}} & {{{if}\mspace{14mu} G_{c}} \leq {G_{N} + {dG}}} \\{Detected} & {{{if}\mspace{14mu} G_{c}} > {G_{N} + {dG}}}\end{matrix} \right.} & (1)\end{matrix}$

Specifically, determining whether the potential fault is detected atstep 240 includes comparing the gain control parameter with the gainthreshold. In response to a comparison result that the gain controlparameter is greater than the gain threshold, step 240 further includesdetermining that the potential fault is detected. In response to acomparison result that the gain control parameter is less than or equalto the gain threshold, step 240 further includes determining that thepotential fault is not detected.

In other words, if the current gain a of PGA 360 is less than or equalto the gain threshold, i.e., G_(c)≤G_(N)+dG, fault detector 140 isconfigured to determine that the potential fault is not detected. If thecurrent gain G_(c) of PGA 360 is greater than the gain threshold, i.e.,G_(c)>G_(N)+dG, fault detector 140 is configured to determine that thepotential fault is detected.

In some embodiments, the gain control parameter obtained at step 220includes a current gain of the PGA in the receiver of the positioningdevice. The gain threshold in step 240 includes a nominal gain of thePGA plus a delta value of gain. For example, the gain control parameterthat fault detector 140 obtains is the current gain G_(c) of PGA 360 inreceiver 120 of positioning device 160. Fault detector 140 compares thecurrent gain G_(c) of PGA 360 with the gain threshold that includes thenominal gain G_(N) of PGA 360 plus the delta value of gain dG.

In some embodiments, the nominal gain in method 200 includes at leastone of a predetermined value of gain stored in the at least one memory,an initialized value of gain obtained from an initialization of thereceiver, or a low-pass filtered value of gain.

For example, controller 142 of fault detector 140 is configured to reada predetermined value of gain stored in memory 144 as the nominal gainG_(N). The predetermined value of gain may be input and stored in memory144 by a user. Alternatively, the predetermined value of gain may be anaverage gain of PGA 360 determined based on signals previously receivedby receiver 120 for positioning.

As another example, controller 142 of fault detector 140 may beconfigured to obtain an initialized value of gain of PGA 360 as thenominal gain G_(N), when receiver 120 is configured to execute aninitialization procedure. When receiver 120 executes the initializationprocedure, AGC 122 is configured to control a gain of PGA 360 to asuitable value that allows receiver 120 to receive signals with suitablesignal strength for positioning. Controller 142 is configured to storethe initialized value of gain as the nominal gain G_(N) in memory 144.Alternatively, controller 142 may be configured to store the initializedvalue of gain as the nominal gain G_(N) in a one-time-programmablememory.

Alternatively, controller 142 of fault detector 140 can be configured toobtain a low-pass filtered value of gain of PGA 360 as the nominal gainG_(N). When AGC 122 adjusts the gain of PGA 360 by a plurality of valuesof gain over a period of time, controller 142 can be configured tolow-pass filter the plurality of values of gain to obtain the low-passfiltered value of gain of PGA 360 as the nominal gain G_(N). Forexample, controller 142 may calculate a running average of the pluralityof values of gain. Controller 142 is configured to store the low-passfiltered value of gain of PGA 360 in memory 144.

In the embodiments described above with reference to FIGS. 1-3, a gainof PGA 360 is considered as varied within the gain threshold when allcomponents of positioning device 160 operate without a fault. PGA 360has a low-pass characteristic. When the gain of PGA 360 increases, anamplification bandwidth of PGA 360 decreases. If the gain of PGA 360increases to a high level, the information about a received signal instep 220 can include information about an estimation of bias due togroup delay variations on the received signal. In particular, anestimation of bias due to group delay variations on positioning signalsclose to band edges, such as BeiDou B1D1 signals in the BeiDouNavigation Satellite System (BDS), GLONASS L1OF and L2OF signals in theglobal navigation satellite system (GLONASS), and Galileo E5b signals inthe Galileo positioning system, can be used in method 200 for detectinga potential fault in a positioning device.

In some embodiments, information about a received signal obtained instep 220 can include information about an inter-channel bias (ICB)estimation between two channels of a positioning system. The detectionthreshold in step 240 includes a first ICB threshold and a second ICBthreshold. The first ICB threshold is greater than the second ICBthreshold. Determining whether the potential fault is detected in step240 includes at least one of: comparing the ICB estimation with thefirst ICB threshold, or comparing the ICB estimation with the second ICBthreshold; and determining that the potential fault is detected inresponse to one of: a comparison result that the ICB estimation isgreater than the first ICB threshold, or a comparison result that theICB estimation is less than the second ICB threshold.

For example, when receiver 120 of positioning device 160 receivesGLONASS signals, signals of different GLONASS frequency divisionmultiple access (FDMA) channels contain different group delays becauseof frequency-dependent distortions in GLONASS signals. For signalcompensation and positioning accuracy, receiver 120 is configured toestimate an ICB between two GLONASS FDMA channels caused by differentgroup delays. In other words, receiver 120 is configured to estimate anICB between first and second GLONASS FDMA channels as an ICB of thefirst channel. The second GLONASS channel can be any one of GLONASS FDMAchannels. The ICB estimation is an estimation of a per-channel delay.

An ICB between two GLONASS FDMA channels may vary but will vary within arange between an upper limit and a lower limit when all components ofpositioning device 160 operate without a fault. However, when a faultexists in one of the components of positioning device 160, the fault maycause an anomalous ICB to be greater than the upper limit or less thanthe lower limit. Thus, fault detector 140 can be configured to practicemethod 200 for detecting a potential fault in one of the components ofpositioning device 160 as described below.

Fault detector 140 is configured to obtain information about an ICBestimation between two GLONASS FDMA channels from navigation engine 128of receiver 120 via connection 123. The ICB estimation is, for example,a current ICB, ICB_(C), of the two GLONASS FDMA channels. Receiver 120has a nominal ICB, ICB_(N), after positioning device 160 is initializedand starts to receive GLONASS signals for positioning. The nominal ICB,ICB_(N), is an ICB between the two GLONASS FDMA channels when allcomponents of positioning device 160 operate without a fault. Thenominal ICB, ICB_(N), can be an average ICB when positioning device 160operates and provides accurate positioning information.

The detection threshold in step 240 includes a first ICB threshold equalto the nominal ICB, ICB_(N), plus a first delta value of ICB, dICB₁,i.e., the first ICB threshold=ICB_(N)+dICB₁. The first delta value dICB₁can be, for example, 3 or 5 centimetres per channel (cm/channel), whichis a first margin to allow variations in an ICB because of varied groupdelays in two different channels. The first ICB threshold is an upperlimit of ICB between the two GLONASS FDMA channels.

The detection threshold in step 240 also includes a second ICB thresholdequal to the nominal ICB, ICB_(N), minus a second delta value of ICB,dICB₂, i.e., the second ICB threshold=ICB_(N)−dICB₂. The second deltavalue dICB₂ can be, for example, 2 or 3 centimetres per channel(cm/channel), which is a second margin to allow for variations in an ICBbecause of varied group delays in two different GLONASS FDMA channels.The second ICB threshold is a lower limit of ICB between the two GLONASSFDMA channels. The first ICB threshold, i.e., the upper limit of ICB, isgreater than the second ICB threshold, i.e., the lower limit of ICB.

Determining whether the potential fault is detected at step 240 includesdetermining whether the current ICB, ICB_(C), between two GLONASS FDMAchannels is above a first ICB threshold or below a second ICB threshold.Mathematically, this may be expressed as:

$\begin{matrix}{{{Potential}\mspace{14mu}{Fault}} = \left\{ \begin{matrix}{{Not}\mspace{14mu}{Detected}} & {{{{if}\mspace{14mu}{ICB}_{N}} - {dICB}_{2}} \leq {ICB}_{C} \leq {{ICB}_{N} + {dICB}_{1}}} \\{Detected} & {{{if}\mspace{14mu}{ICB}_{C}} > {{ICB}_{N} + {{dICB}_{1}\mspace{14mu}{or}\mspace{14mu}{ICB}_{C}}} < {{ICB}_{N} - {dICB}_{2}}}\end{matrix} \right.} & (2)\end{matrix}$

Specifically, determining whether the potential fault is detected instep 240 includes comparing the current ICB, ICB_(C), with the first ICBthreshold ICB_(N)+dICB₁. In response to a comparison result that thecurrent ICB is greater than the first ICB threshold, i.e.,ICB_(C)>ICB_(N)+dICB₁, step 240 further includes determining that thepotential fault is detected.

In response to a comparison result that the current ICB is less than orequal to the first ICB threshold, step 240 includes comparing thecurrent ICB, ICB_(C), with the second ICB threshold ICB_(N)−dICB₂. Inresponse to a comparison result that the current ICB is less than thesecond ICB threshold, i.e., ICB_(C)<ICB_(N)−dICB₂, step 240 furtherincludes determining that the potential fault is detected.

In response to a comparison result that the current ICB is less than orequal to the first ICB threshold and greater than or equal to the secondICB threshold, step 240 further includes determining that the potentialfault is not detected.

In step 240, either one of the comparisons between the current ICB andthe first ICB threshold and between the current ICB and the second ICBthreshold can be performed before the other. When one of the comparisonsresults in a determination that the potential fault is detected, theother comparison may not be performed.

In other words, if the current ICB, ICB_(C), is greater than the firstICB threshold ICB_(N)+dICB₁, or less than the second ICB thresholdICB_(N)−dICB₂, fault detector 140 is configured to determine that apotential fault is detected in positioning device 160. If the currentICB, ICB_(C), is less than or equal to the first ICB thresholdICB_(N)+dICB₁, and greater than or equal to the second ICB thresholdICB_(N)−dICB₂, fault detector 140 is configured to determine that thepotential fault is not detected in positioning device 160.

In some embodiments, the nominal ICB in method 200 includes at least oneof a predetermined value of ICB stored in the at least one memory, aninitialized value of ICB obtained from an initialization of a receiverof the positioning device, or a low-pass filtered value of ICB.

For example, controller 142 of fault detector 140 may be configured toread a predetermined value of ICB stored in memory 144 as the nominalICB, ICB_(N). The predetermined value of ICB may be input and stored inmemory 144 by a user. Alternatively, the predetermined value of ICB maybe an average ICB determined based on signals previously received byreceiver 120 for positioning.

As another example, controller 142 of fault detector 140 may beconfigured to obtain an initialized value of ICB as the nominal ICB,ICB_(N), when receiver 120 is configured to execute an initializationprocedure. When receiver 120 executes the initialization procedure,navigation engine 128 is configured to estimate an ICB between twoGLONASS FDMA channels. Controller 142 is configured to store theinitialized value of ICB as the nominal ICB, ICB_(N), in memory 144.Alternatively, controller 142 may be configured to store the initializedvalue of ICB as the nominal ICB, ICB_(N), in a one-time-programmablememory.

Alternatively, controller 142 of fault detector 140 can be configured toobtain a low-pass filtered value of ICB as the nominal ICB, ICB_(N).When navigation engine 128 estimates a plurality of values of ICBbetween the two GLONASS FDMA channels over a period of time, controller142 can be configured to low-pass filter the plurality of values of ICBto obtain the low-pass filtered value of ICB as the nominal ICB,ICB_(N). For example, controller 142 may calculate a running average ofthe plurality of values of ICB. Controller 142 is configured to storethe low-pass filtered value of ICB in memory 144.

In some embodiments, the ICB estimation in method 200 includes anestimation of group delay between the two channels of the positioningsystem. For example, the ICB estimation in method 200 is an estimationof group delay between two channels of the GLONASS. Alternatively, theICB estimation in method 200 may be an estimation of group delay betweentwo channels of other satellite positioning systems.

In some embodiments, the received signal in step 220 is a first receivedsignal from a first positioning system and the positioning device isconfigured to receive a second received signal from a second positioningsystem. In such embodiments, the information in step 220 includes aninter-system bias (ISB) estimation between the first and secondpositioning systems based on the first and second received signals. Thedetection threshold in step 240 includes a first ISB threshold and asecond ISB threshold. The first ISB threshold is greater than the secondISB threshold. Determining whether the potential fault is detected atstep 240 includes at least one of: comparing the ISB estimation with thefirst ISB threshold, or comparing the ISB estimation with the second ISBthreshold; and determining that the potential fault is detectedresponsive to one of: a comparison result that the ISB estimation isgreater than the first ISB threshold, or a comparison result that theISB estimation is less than the second ISB threshold.

For example, when receiver 120 of positioning device 160 is configuredto receive GLONASS and Galileo signals, GLONASS and Galileo signalscontain different group delays because of frequency-dependentdistortions in the signals at different frequencies. For instance,receiver 120 is configured to receive GLONASS L1OF signals at 1598.1 to1605.4 MHz and Galileo E1BC signals at 1575 MHz. Alternatively, receiver120 of positioning device 160 may be configured to receive GPS L1signals at 1575 MHz, BeiDou B1D1 signals at 1559 MHz, Galileo E1BCsignals at 1575 MHz, GLONASS L1OF signals at 1598.1 MHz to 1605.4 MHz,or GPS L2C signals at 1227 MHz, BeiDou B2I signals at 1207 MHz, GalileoE5b signals at 1207 MHz, GLONASS L2OF signals at 1242.9 and 1248.6 MHz.For signal compensation and positioning accuracy, positioning device 160is configured to estimate an ISB between signals of two GNSSconstellations caused by different group delays. The estimated ISB is aninter-GNSS bias caused by group delay variations in the signals of thetwo GNSS constellations.

An ISB between signals of two different GNSS constellations may vary butremain within a range between an upper limit and a lower limit when allcomponents of positioning device 160 operate without a fault. However,when a fault exists in one of the components of positioning device 160,the fault may cause an anomalous ISB that is greater than the upperlimit or less than the lower limit. Thus, fault detector 140 can beconfigured to practice method 200 for detecting a potential fault in oneof the components of positioning device 160 as described below.

Fault detector 140 is configured to obtain information about an ISBestimation between signals of two GNSS constellations from receiver 120of positioning device 160 via connection 123. The ISB estimation is, forexample, a current ISB, ISB_(C), of the signals of the two GNSSconstellations. Positioning device 160 obtains a nominal ISB, ISB_(N),after positioning device 160 is initialized and starts to receivesignals of the two GNSS constellations for positioning. The nominal ISB,ISB_(N), is an ISB between signals of the two GNSS constellations whenall components of positioning device 160 operate without a fault. Thenominal ISB, ISB_(N), can be an average ISB when positioning device 160operates and provides accurate positioning information.

The detection threshold in step 240 includes a first ISB threshold equalto the nominal ISB, ISB_(N), plus a first delta value of ISB, dISB₁,i.e., the first ISB threshold=ISB_(N)+dISB₁. The first delta value dISB₁can be, for example, 50 or 60 centimetres per system (cm/system), whichis a first margin to allow variations in an ISB because of varied groupdelays in the signals of the two GNSS constellations. The first ISBthreshold is an upper limit of ISB between the signals of the two GNSSconstellations.

The detection threshold in step 240 also includes a second ISB thresholdequal to the nominal ISB, ISB_(N), minus a second delta value of ISB,dISB₂, i.e., the second ISB threshold=ISB_(N)−dISB₂. The second deltavalue dISB₂ can be, for example, 40 or 50 centimetres per system(cm/system), which is a second margin to allow for variations in an ISBbecause of varied group delays in the signals of the two GNSSconstellations. The second ISB threshold is a lower limit of ISB betweenthe signals of the two GNSS constellations. The first ISB threshold,i.e., the upper limit of ISB, is greater than the second ISB threshold,i.e., the lower limit of ISB.

Determining whether the potential fault is detected at step 240 includesdetermining whether the current ISB, ISB_(C), between two GNSSconstellations is above a first ISB threshold or below a second ISBthreshold. Mathematically, this may be expressed as:

$\begin{matrix}{{{Potential}\mspace{14mu}{Fault}} = \left\{ \begin{matrix}{{Not}\mspace{14mu}{Detected}} & {{{{if}\mspace{14mu}{ISB}_{N}} - {dISB}_{2}} \leq {ISB}_{C} \leq {{ISB}_{N} + {dISB}_{1}}} \\{Detected} & {{{if}\mspace{14mu}{ISB}_{C}} > {{ISB}_{N} + {{dISB}_{1}\mspace{14mu}{or}\mspace{14mu}{ISB}_{C}}} < {{ISB}_{N} - {dISB}_{2}}}\end{matrix} \right.} & (3)\end{matrix}$

Specifically, determining whether the potential fault is detected instep 240 includes comparing the current ISB, ISB_(C), with the first ISBthreshold ISB_(N)+dISB₁. In response to a comparison result that thecurrent ISB is greater than the first ISB threshold, i.e.,ISB_(C)>ISB_(N)+dISB₁, step 240 further includes determining that thepotential fault is detected.

In response to a comparison result that the current ISB is less than orequal to the first ISB threshold, step 240 includes comparing thecurrent ISB, ISB_(C), with the second ISB threshold ISB_(N)−dISB₂. Inresponse to a comparison result that the current ISB is less than thesecond ICB threshold, i.e., ISB_(C)<ISB_(N)−dISB₂, step 240 furtherincludes determining that the potential fault is detected.

In response to a comparison result that the current ISB is less than orequal to the first ISB threshold and greater than or equal to the secondISB threshold, i.e., ISB_(N)−dISB₂≤ISB_(C)≤ISB_(N)+dISB₁, step 240further includes determining that the potential fault is not detected.

In step 240, either one of the comparisons between the current ISB andthe first ISB threshold and between the current ISB and the second ISBthreshold can be performed before the other. When one of the comparisonsresults in a determination that the potential fault is detected, theother comparison may not be performed. Alternatively, when one of thecomparisons results in a determination that the potential fault isdetected, the other comparison may still be performed.

In other words, if the current ISB, ISB_(C), is greater than the firstISB threshold ISB_(N)+dISB₁, or less than the second ISB thresholdISB_(N)−dISB₂, fault detector 140 is configured to determine that apotential fault is detected in positioning device 160. If the currentISB, ISB_(C), is less than or equal to the first ISB thresholdISB_(N)+dISB₁, and greater than or equal to the second ISB thresholdISB_(N)−dISB₂, fault detector 140 is configured to determine that thepotential fault is not detected in positioning device 160.

In some embodiments, the nominal ISB in method 200 includes at least oneof a predetermined value of ISB stored in the at least one memory, aninitialized value of ISB obtained from an initialization of a receiverof the positioning device, or a low-pass filtered value of ISB.

For example, controller 142 of fault detector 140 is configured to reada predetermined value of ISB stored in memory 144 as the nominal ISB,ISB_(N). The predetermined value of ISB may be input and stored inmemory 144 by a user. Alternatively, the predetermined value of ISB maybe an average ISB determined based on signals previously received byGNSS receiver 452 and GNSS receiver 454 for positioning.

As another example, controller 142 of fault detector 140 may beconfigured to obtain an initialized value of ISB as the nominal ISB,ISB_(N), when receiver 120 of positioning device 160 is configured toexecute an initialization procedure. When receiver 120 executes theinitialization procedure, receiver 120 is configured to estimate an ISBbetween signals of two GNSS constellations. Controller 142 is configuredto store the initialized value of ISB as the nominal ISB, ISB_(N), inmemory 144. Alternatively, controller 142 may be configured to store theinitialized value of ISB as the nominal ISB, ISB_(N), in aone-time-programmable memory.

Alternatively, controller 142 of fault detector 140 can be configured toobtain a low-pass filtered value of ISB as the nominal ISB, ISB_(N).When receiver 120 estimates a plurality of values of ISB between the twoGNSS constellations over a period of time, controller 142 can beconfigured to low-pass filter the plurality of values of ISB to obtainthe low-pass filtered value of ISB as the nominal ISB, ISB_(N). Forexample, controller 142 may calculate a running average of the pluralityof values of ISB. Controller 142 is configured to store the low-passfiltered value of ISB in memory 144.

In some embodiments, the ISB estimation in step 220 is a first ISBestimation. The positioning device is configured to receive a thirdreceived signal from a third positioning system. The information in step220 further includes a second ISB estimation between the first and thirdpositioning systems based on the first and third received signals. Thedetection threshold in step 240 further includes a third ISB thresholdand a fourth ISB threshold, the third ISB threshold being greater thanthe fourth ISB threshold. Determining whether the potential fault isdetected at step 240 further includes at least one of: comparing thesecond ISB estimation with the third ISB threshold, or comparing thesecond ISB estimation with the fourth ISB threshold; and determiningthat the potential fault is detected responsive to one of: a comparisonresult that the second ISB estimation is greater than the third ISBthreshold, or a comparison result that the second ISB estimation is lessthan the fourth ISB threshold.

For example, receiver 120 of positioning device 160 may be configured toreceive global positioning system (GPS) and BeiDou signals. Positioningdevice 160 is configured to estimate a first ISB between the GPS andBeiDou signals caused by different group delays, as described above withreference to equation (3). In addition, receiver 120 of positioningdevice 160 is also configured to receive GLONASS signals. Positioningdevice 160 is configured to estimate a second ISB between the GPS andGLONASS signals caused by different group delays, similar todescriptions above with reference to equation (3).

Fault detector 140 is configured to compare the first ISB estimationwith a first ISB threshold, or compare the first ISB estimation with asecond ISB threshold, as described above with reference to equation (3).Fault detector 140 is also configured to compare the second ISBestimation with a third ISB threshold, or compare the second ISBestimation with a fourth ISB threshold, similar to descriptions abovewith reference to equation (3). Fault detector 140 is configured todetermine that the potential fault is detected responsive to one of: acomparison result that the first ISB estimation is greater than thefirst ISB threshold, or a comparison result that the first ISBestimation is less than the second ISB threshold, or a comparison resultthat the second ISB estimation is greater than the third ISB threshold,or a comparison result that the second ISB estimation is less than thefourth ISB threshold.

In some embodiments, the received signal in step 220 is a first receivedsignal from a first positioning system. The positioning device, e.g.,positioning device 160, is configured to receive a plurality of receivedsignals from a plurality of positioning systems including the firstpositioning system. The received signals include the first receivedsignal. The information in step 220 includes a multiple globalnavigation satellite system (multi-GNSS) estimation. The multi-GNSSestimation includes a plurality of inter-system bias (ISB) estimationscorresponding to a plurality of pairs of the positioning systems. Thedetection threshold in step 240 includes a first multi-GNSS ISBthreshold, a second multi-GNSS ISB threshold, a first system-numberthreshold, and a second system-number threshold. The first multi-GNSSISB threshold includes a plurality of first ISB thresholds correspondingto the pairs of the positioning systems. The second multi-GNSS ISBthreshold includes a plurality of second ISB thresholds corresponding tothe pairs of the positioning systems. The first ISB thresholds arerespectively greater than the corresponding second ISB thresholds.Determining whether the potential fault is detected in step 240 includes(i) at least one of: (a) comparing the ISB estimations between theplurality of pairs of positioning systems with the first ISB thresholds,respectively; and determining that the multi-GNSS ISB estimation isgreater than the first multi-GNSS ISB threshold when a number ofcomparison results that the ISB estimations are greater than the firstISB thresholds is greater than the first system-number threshold; or (b)comparing the ISB estimations with the second ISB thresholds,respectively; and determining that the multi-GNSS ISB estimation is lessthan the second multi-GNSS ISB threshold when a number of comparisonresults that the ISB estimations are less than the second ISB thresholdsis greater than the second system-number threshold; and (ii) determiningthat the potential fault is detected, responsive to at least one of: adetermination that the multi-GNSS ISB estimation is greater than thefirst multi-GNSS ISB threshold; or a determination that the multi-GNSSISB estimation is less than the second multi-GNSS ISB threshold.

For example, positioning device 160 is configured to receive a GLONASSsignal as described above with reference to FIG. 1. The received GLONASSsignal is a first GLONASS signal from a first positioning system, i.e.,the GLONASS system. Receiver 120 of positioning device 160 can beconfigured to respectively receive the first GLONASS signal and a firstGalileo signal. The first GLONASS and first Galileo signals containdifferent group delays because of frequency-dependent distortions in thesignals at different frequencies. For signal compensation andpositioning accuracy, positioning device 160 is configured to estimate afirst ISB between the two first signals of the two GNSS constellationscaused by different group delays. The estimated first ISB is a firstinter-GNSS bias caused by group delay variations in the first GLONASSand first Galileo signals.

Receiver 120 of positioning device 160 is configured to respectivelyreceive second GLONASS and second Galileo signals. Similarly,positioning device 160 is configured to estimate a second ISB betweenthe second GLONASS and second Galileo signals caused by different groupdelays. In this manner, positioning device 160 is configured to receivea plurality of received signals from the GLONASS and Galileo systems,including the first positioning system, i.e., the GLONASS system.

Receiver 120 of positioning device 160 is configured to respectivelyreceive third GLONASS and third Galileo signals. Similarly, positioningdevice 160 is configured to estimate a third ISB between the thirdGLONASS and third Galileo signals caused by different group delays. Inthis manner, positioning device 160 is configured to receive a pluralityof received signals from the GLONASS and Galileo systems, including thefirst positioning system, i.e., the GLONASS system. Positioning device160 is configured to estimate a plurality of ISBs corresponding to aplurality of pairs of GLONASS and Galileo systems. Alternatively,receiver 120 of positioning device 160 can also be configured torespectively receive Galileo and BeiDou signals. Positioning device 160is configured to estimate an ISB between the Galileo and BeiDou signalscaused by different group delays. Moreover, receiver 120 of positioningdevice 160 can be configured to respectively receive BeiDou and globalpositioning system (GPS) signals. Positioning device 160 is configuredto estimate an ISB between the BeiDou and GPS signals caused bydifferent group delays. In this manner, the plurality of receivedsignals received by positioning device 160 can be from a plurality ofpositioning systems, such as GLONASS, Galileo, BeiDou, and GPS systems.Thus, positioning device 160 is configured to estimate a plurality ofISBs corresponding to a plurality of pairs of positioning systems.

Similar to the ISB_(C) in equation (3), each of the plurality of ISBsbetween two GNSS signals may vary but remain within a range between anupper limit and a lower limit when all components of positioning device160 operate without a fault. However, a fault in one of the componentsof positioning device 160 may cause an anomalous ISB that is greaterthan the upper limit or less than the lower limit. Thus, fault detector140 can be configured to practice method 200 for detecting a potentialfault in one of the components of positioning device 160 as describedbelow.

Moreover, as another example, receiver 120 of positioning device 160 maybe configured to receive global positioning system (GPS) and BeiDousignals. Positioning device 160 is configured to estimate an ISB betweenthe GPS and BeiDou signals caused by different group delays. Inaddition, receiver 120 of positioning device 160 is also configured toreceive GPS and GLONASS signals. Positioning device 160 is configured toestimate an ISB between the GPS and GLONASS signals caused by differentgroup delays. In this manner, the plurality of received signals receivedby positioning device 160 can be from a plurality of positioningsystems, such as GPS, GLONASS, Galileo, and BeiDou systems. Positioningdevice 160 is configured to estimate a plurality of ISBs correspondingto a plurality of pairs of positioning systems. Each of the plurality ofpairs of positioning systems includes the GPS system and anotherpositioning system, such as the BeiDou or GLONASS system.

Fault detector 140 is configured to obtain information about theplurality of inter-system bias (ISB) estimations corresponding to theplurality of pairs of the positioning systems from receiver 120 viaconnection 123. For example, fault detector 140 is configured to obtainthe plurality of ISB estimations corresponding to the plurality of pairsof the positioning systems. The plurality of ISB estimations are, forexample, a plurality of current ISBs, ISB_(Ci), of signals of the GNSSconstellations, i=0, 1, 2, . . . , SP−1, where SP is a total number ofthe pairs of the positioning systems. One of the pairs of thepositioning systems may include the same or different two positioningsystems as another one of the pairs of the positioning systems. Theplurality of current ISBs, ISB_(Ci), are collectively defined as amulti-GNSS ISB estimation.

Positioning device 160 obtains a plurality of nominal ISBs, ISB_(Ni),i=0, 1, 2, . . . , SP−1, after positioning device 160 is initialized andstarts to receive signals of the GNSS constellations for positioning.The plurality of nominal ISBs, ISB_(Ni), are ISBs between signals of theplurality of pairs of GNSS constellations when all components ofpositioning device 160 operate without a fault. The nominal ISBs,ISB_(Ni), can be average ISBs when positioning device 160 operates toprovide an accurate position.

The detection threshold in step 240 includes a plurality of first ISBthresholds equal to the nominal ISBs, ISB_(Ni), plus a plurality offirst delta values of ISB, dISB_(1i), respectively, i.e., the first ISBthreshold for the i^(th) pair of GNSS constellations=ISB_(Ni)+dISB_(1i),i=0, 1, 2, . . . , SP−1. The plurality of first delta values dISB_(1i)can respectively be, for example, 4 or 5 centimetres per pair of systems(cm/pair), which are a plurality of first margins to allow variations inISBs in the plurality of pairs of GNSS constellations because of variedgroup delays. The plurality of first ISB thresholds are upper limits ofISB between two GNSS signals in each pair of GNSS constellations,respectively. The plurality of first ISB thresholds ISB_(Ni)+dISB_(1i),i=0, 1, 2, . . . , SP−1, are collectively defined as a first multi-GNSSthreshold.

The detection threshold in step 240 also includes a plurality of secondISB thresholds equal to the nominal ISBs, ISB_(Ni), minus a plurality ofsecond delta values of ISB, dISB_(2i), i.e., the second ISBthresholds=ISB_(Ni)−dISB_(2i), i=0, 1, 2, . . . , SP−1. The plurality ofsecond delta values dISB_(2i) can respectively be, for example, 4 or 5centimetres per pair (cm/system), which are a plurality of secondmargins to allow variations in ISBs in the plurality of pairs of GNSSconstellations because of varied group delays. The plurality of secondISB thresholds are lower limits of ISB between two GNSS signals in eachpair of GNSS constellations, respectively. The plurality of second ISBthresholds ISB_(Ni)−dISB_(2i), i=0, 1, 2, . . . , SP−1, are collectivelydefined as a second multi-GNSS threshold. The plurality of first ISBthresholds, i.e., the upper limits of ISB, are respectively greater thanthe plurality of second ISB thresholds, i.e., the lower limits of ISB.

Determining whether the potential fault is detected at step 240 includesdetermining:

$\begin{matrix}{{{Potential}\mspace{14mu}{Fault}} = \left\{ \begin{matrix}{Detected} & {{{if}\mspace{14mu}{ISB}_{Ci}} > {{ISB}_{Ni} + {{dISB}_{1i}\mspace{14mu}{for}\mspace{14mu}{SN}\; 1\mspace{14mu}{pairs}}}} \\{Detected} & {{{if}\mspace{14mu}{ISB}_{Ci}} < {{ISB}_{Ni} - {{dISB}_{2i}\mspace{14mu}{for}\mspace{14mu}{SN}\; 2\mspace{14mu}{pairs}}}}\end{matrix} \right.} & (4)\end{matrix}$

If neither SN1 pairs nor SN2 pairs are achieved in accordance with theabove conditions, determining whether the potential fault is detected atstep 240 includes determining that the potential fault is Not Detected,where SN1 and SN2 are first and second system-number thresholds.

Specifically, determining whether the potential fault is detected instep 240 includes comparing the current ISBs, ISB_(Ci), with the firstISB thresholds ISB_(Ni)+dISB_(1i), respectively. In response to a firstnumber of comparison results that the ISB estimations are greater thanthe first ISB thresholds is greater than or equal to a firstsystem-number threshold, SN1, i.e., ISB_(Ci)>ISB_(Ni)+dISB_(1i) for SN1or more pairs, step 240 further includes determining that a multipleGNSS (multi-GNSS) ISB estimation is greater than the first multi-GNSSISB threshold.

In response to the first number of comparison results that the ISBestimations are greater than the first ISB thresholds is less than thefirst pair number threshold SN1, step 240 further includes determiningthat the multi-GNSS ISB estimation is less than the first multi-GNSS ISBthreshold.

In response to the first number of comparison results that the ISBestimations are greater than the first ISB thresholds is less than thefirst pair number threshold SN1, step 240 includes comparing the currentISBs, ISB_(Ci), with the second ISB thresholds ISB_(Ni)−dISB_(2i),respectively. In response to a second number of comparison results thatthe ISB estimations are less than the second ISB thresholds is greaterthan or equal to a second system-number threshold SN2, i.e.,ISB_(Ci)<ISB_(Ni)−dISB_(2i) for SN2 or more pairs, step 240 furtherincludes determining that the multi-GNSS ISB estimation is less than thesecond multi-GNSS ISB threshold.

In response to the second number of comparison results that the ISBestimations are less than the second ISB thresholds is less than thesecond pair number threshold SN2, step 240 further includes determiningthat the multi-GNSS ISB estimation is greater than the second multi-GNSSISB threshold.

In some embodiments, in step 240, either the comparisons between thecurrent ISBs and the first ISB thresholds or the comparisons between thecurrent ISBs and the second ISB thresholds may be performed before theother. When either of the comparisons are performed, the other of thecomparisons may not be performed. Alternatively, when either of thecomparisons are performed, the other of the comparisons may still beperformed.

Moreover, step 240 further includes determining that the potential faultis detected in response to at least one of: a determination that themulti-GNSS ISB estimation is greater than the first multi-GNSS ISBthreshold, or a determination that the multi-GNSS ISB estimation is lessthan the second multi-GNSS ISB threshold.

In other words, if the first number of comparison results that the ISBestimations are greater than the first ISB thresholds is greater than orequal to the first system-number threshold SN1, i.e.,ISB_(Ci)>ISB_(Ni)+dISB_(1i) for SN1 or more pairs, fault detector 140 isconfigured to determine that a potential fault is detected inpositioning device 160. If the second number of comparison results thatthe ISB estimations are less than the second ISB thresholds is greaterthan or equal to the second system-number threshold SN2, i.e.,ISB_(Ci)<ISB_(Ni)−dISB_(2i) for SN2 or more pairs, fault detector 140 isconfigured to determine that a potential fault is detected inpositioning device 160.

In some embodiments, fault detector 140 can be configured to compare theISB estimations with the first or second ISB thresholds until SN1 or SN2pair is achieved as described in equation (4) and determine that apotential fault is detected in positioning device 160. Fault detector140 may not be configured to compare the remaining ISB estimations withthe remaining first or second ISB thresholds.

In some embodiments, fault detector 140 is configured to compare the ISBestimations with one or more of the first ISB thresholds and one or moreof the second ISB thresholds until a third system-number threshold SN3is achieved. If a sum of (a) a first number of comparison results thatthe ISB estimations are greater than the first ISB thresholds and (b) asecond number of comparison results that the ISB estimations are lessthan the second ISB thresholds, is greater than or equal to the thirdsystem-number threshold SN3, fault detector 140 is configured todetermine that a potential fault is detected in positioning device 160.

In some embodiments, the nominal ISBs in method 200 include at least oneof predetermined values of ISB stored in the at least one memory,initialized values of ISB obtained from an initialization of thepositioning device, or low-pass filtered values of ISB, similar to thenominal ISB described above with reference to equation (3).

FIG. 4 is a block diagram of an exemplary positioning device 400,consistent with embodiments of the present disclosure. As shown in FIG.4, positioning device 400 includes a diplexer 410, first and secondimpedance matching networks (IMNs) 422 and 424, first and second filters432 and 434, third and fourth impedance matching networks (IMNs) 442 and444, and first and second global navigation satellite system (GNSS)chips 452 and 454. Diplexer 410 includes a high-pass filter (HPF) 412and a low-pass filter (LPF) 414. HPF 412 of diplexer 410, firstimpedance matching network (IMN) 422, first filter 432, third impedancematching network (IMN) 442, and first GNSS chip 452 are coupled incascade to form a first RF path 460 for receiving satellite signals in afirst frequency band. LPF 414 of diplexer 410, second impedance matchingnetwork (IMN) 424, second filter 434, fourth impedance matching network(IMN) 444, and second GNSS chip 454 are coupled in cascade to form asecond RF path 470 for receiving satellite signals in a second frequencyband.

Diplexer 410 is configured to receive signals via an input 401 ofpositioning device 400 and filter the signals in the first and secondfrequency bands for first and second RF paths 460 and 470, respectively.In first RF path 460, HPF 412, first impedance matching network (IMN)422, first filter 432, and third impedance matching network (IMN) 442are configured to filter and process signals in the first frequency bandfor first GNSS chip 452 to track, demodulate and decode messages fromsatellites. Similarly, in second RF path 470, LPF 414, second impedancematching network (IMN) 424, second filter 434, and fourth impedancematching network (IMN) 444 are configured to filter and process signalsin the second frequency band for second GNSS chip 454 to track,demodulate and decode messages from satellites.

In FIG. 4, impedance matching networks (IMNs) 422, 442, 424 and 444 areshown as separate blocks. A person skilled in the art, however, willappreciate that any one of these networks may instead be included aspart of the preceding or succeeding block. For example, impedancematching network (IMN) 442 may instead be part of first filter 432 orGNSS chip 452. Similarly, impedance matching network (IMN) 424 mayinstead be included as part of LPF 414 or second filter 434.

First and second GNSS chips 452 and 454 are configured to exchangesignals and/or data on two bands via a connection 405. For example,first and second RF paths 460 and 470 may be configured to receive GPSsignals on L1 and L2 bands, respectively. GNSS chip 452 can beconfigured to acquire signals and/or data on the L2 band from GNSS chip454 via connection 405. GNSS chip 452 is configured to send resultsand/or data of positioning device 400 to an external device via anoutput 403.

FIG. 5 is a block diagram of an exemplary antenna subsystem 500 of apositioning device, consistent with embodiments of the presentdisclosure. Antenna subsystem 500 is a dual-band GNSS antenna subsystem.As shown in FIG. 5, antenna subsystem 500 includes two antenna RF paths.A first of the two antenna RF paths includes antennas 501 and 502, afirst hybrid coupler 512, a first resistor 513, a first filter 522, afirst impedance matching network (IMN) 532, a first low-noise amplifier(LNA) 533, a second impedance matching network (IMN) 542, a secondfilter 552, a third impedance matching network (IMN) 562, a second LNA563, and a fourth impedance matching network (IMN) 572, all coupled incascade. The second antenna RF path includes antennas 503 and 504, asecond hybrid coupler 514, a second resistor 515, a third filter 524, afifth impedance matching network (IMN) 534, a third LNA 535, a sixthimpedance matching network (IMN) 544, a fourth filter 554, a seventhimpedance matching network (IMN) 564, a fourth LNA 565, and an eighthimpedance matching network (IMN) 574, all coupled in cascade. The firstand second antenna RF paths are coupled to a diplexer 580. Diplexer 580includes a low-pass filter (LPF) 582 and a high-pass filter (HPF) 584.

In FIG. 5, impedance matching networks (IMNs) 532, 542, 562 and 572 ofthe first RF path and impedance matching networks (IMNs) 534, 544, 564and 574 of the second RF path are shown as separate blocks. A personskilled in the art, however, will appreciate that any one of thesenetworks may instead be incorporated as part of a preceding orsucceeding block. For example, impedance matching network (IMN) 532 mayinstead be included as part of first filter 522 or first LNA 533.

LPF 582 and HPF 584 of diplexer 580 are coupled to fourth impedancematching network (IMN) 572 and eighth impedance matching network (IMN)574, respectively. When the first and second antenna RF pathsrespectively receive signals on two frequency bands, diplexer 580 isconfigured to combine the signals on the two frequency bands into onedual-band RF signal at an output 505 of antenna subsystem 500.

Dual-band GNSS antenna subsystem 500 can be coupled to dual-bandpositioning device 400 by connecting output 505 to input 401. Diplexer410 is configured to filter the combined dual-band RF signal for firstand second RF paths 460 and 470 to process. In this manner, positioningdevice 400 can be configured to process dual-band signals throughdual-band GNSS antenna subsystem 500.

Positioning device 400 can further include a fault detector, similar tofault detector 140 of positioning device 160. The fault detector ofpositioning device 400 can be configured to practice method 200 fordetecting a potential fault in dual-band positioning device 400.

Alternatively, positioning device 160 can include two RF paths aspositioning device 400. The implementation of dual-band positioningdevice 160 can be configured as dual-band positioning device 400 coupledto antenna subsystem 500, as described above. Fault detector 140 can beconfigured to practice method 200 for detecting a potential fault inpositioning device 160 with two RF paths for two frequency bands. Forconvenience of description, positioning device 160 is described as adual-band positioning device below.

In some embodiments, the information in step 220 includes an inter-bandbias (IBB) estimation between two frequency bands of the positioningsystem. The detection threshold in step 240 includes a first IBBthreshold and a second IBB threshold. The first IBB threshold is greaterthan the second IBB threshold. Determining whether the potential faultis detected in step 240 includes at least one of: comparing the IBBestimation with the first IBB threshold, or comparing the IBB estimationwith the second IBB threshold; and determining that the potential faultis detected in response to one of: a comparison result that the IBBestimation is greater than the first IBB threshold, or a comparisonresult that the IBB estimation is less than the second IBB threshold.

For example, when positioning device 160 is configured to receive GPSsignals on L1 and L2 frequency bands, GPS L1 and L2 signals containdifferent group delays because of frequency-dependent distortions in thesignals on the two different frequency bands. For signal compensationand positioning accuracy, positioning device 160 is configured toestimate an IBB between signals on the GPS L1 and L2 frequency bandscaused by different group delays.

Generally, an IBB between signals on two frequency bands may vary butremain within a range between an upper limit and a lower limit when allcomponents of positioning device 160 operate without a fault. However,when a fault exists in one of the components of positioning device 160,the fault may cause an anomalous IBB that is greater than the upperlimit or less than the lower limit. Thus, fault detector 140 can beconfigured to practice method 200 for detecting a potential fault in oneof the components of positioning device 160 as described below.

Fault detector 140 is configured to obtain information about an IBBestimation between signals on two frequency bands from receiver 120 viaconnection 123. The IBB estimation is, for example, a current IBB,IBB_(C), between signals on the GPS L1 and L2 frequency bands.Positioning device 160 obtains a nominal IBB, IBB_(N), after positioningdevice 160 is initialized and starts to receive signals on GPS L1 and L2frequency bands for positioning. The nominal IBB, IBB_(N), is an IBBbetween the signals on the GPS L1 and L2 frequency bands when allcomponents of positioning device 160 operate without a fault. Thenominal IBB, IBB_(N), can be an average IBB when positioning device 160operates and provides accurate positioning information.

Fault detector 140 can be configured to obtain from memory 144 a firstIBB threshold equal to the nominal IBB, IBB_(N), plus a first deltavalue of IBB, dIBB₁, i.e., the first IBB threshold=IBB_(N)+dIBB₁. Thefirst delta value dIBB₁ can be, for example, 20 or 30 centimetres perband (cm/band), which is a first margin to allow variations in an IBBbecause of varied group delays in the signals on the GPS L1 and L2frequency bands. The first IBB threshold is an upper limit of IBBbetween the signals on GPS L1 and L2 frequency bands.

Fault detector 140 is configured to obtain from memory 144 a second IBBthreshold equal to the nominal IBB, IBB_(N), minus a second delta valueof IBB, dIBB₂, i.e., the second IBB threshold=IBB_(N)−dIBB₂. The seconddelta value of IBB dIBB₂ can be, for example, 40 or 50 centimetres perband (cm/band), which is a second margin to allow variations in an IBBbecause of varied group delays in the signals on GPS L1 and L2 frequencybands. The second IBB threshold is a lower limit of IBB between thesignals on the GPS L1 and L2 frequency bands. The first IBB threshold,i.e., the upper limit of IBB, is greater than the second IBB threshold,i.e., the lower limit of IBB.

Determining whether the potential fault is detected at step 240 includesdetermining whether the current IBB, IBB_(C), between the two GNSSfrequency bands is above a first IBB threshold or below a second IBBthreshold. Mathematically, this may be expressed as:

$\begin{matrix}{{{Potential}\mspace{14mu}{Fault}} = \left\{ \begin{matrix}{{Not}\mspace{14mu}{Detected}} & {{{{if}\mspace{14mu}{IBB}_{N}} - {dIBB}_{2}} \leq {IBB}_{C} \leq {{IBB}_{N} + {dIBB}_{1}}} \\{Detected} & {{{if}\mspace{14mu}{IBB}_{C}} > {{IBB}_{N} + {{dIBB}_{1}\mspace{14mu}{or}\mspace{14mu}{IBB}_{C}}} < {{IBB}_{N} - {dIBB}_{2}}}\end{matrix} \right.} & (5)\end{matrix}$

Specifically, determining whether the potential fault is detected instep 240 includes comparing the current IBB, IBB_(C), with the first IBBthreshold IBB_(N)+dIBB₁. In response to a comparison result that thecurrent IBB is greater than the first IBB threshold, i.e.,IBB_(C)>IBB_(N)+dIBB₁, step 240 further includes determining that thepotential fault is detected.

In response to a comparison result that the current IBB is less than orequal to the first IBB threshold, step 240 includes comparing thecurrent IBB, IBB_(C), with the second IBB threshold IBB_(N)−dIBB₂. Inresponse to a comparison result that the current IBB is less than thesecond IBB threshold, i.e., IBB_(C)<IBB_(N)−dIBB₂, step 240 furtherincludes determining that the potential fault is detected.

In response to a comparison result that the current IBB is less than orequal to the first IBB threshold and greater than or equal to the secondIBB threshold, i.e., IBB_(N)−dIBB₂≤IBB_(C)≤IBB_(N)+dIBB₁, step 240further includes determining that the potential fault is not detected.

In step 240, either one of the comparisons between the current IBB andthe first IBB threshold and between the current IBB and the second IBBthreshold can be performed before the other. When one of the comparisonsresults in a determination that the potential fault is detected, theother comparison may not be performed. Alternatively, when one of thecomparisons results in a determination that the potential fault isdetected, the other comparison may still be performed.

In other words, if the current IBB, IBB_(C), is greater than the firstIBB threshold IBB_(N)+dIBB₁, or less than the second IBB thresholdIBB_(N)−dIBB₂, fault detector 140 is configured to determine that apotential fault is detected in positioning device 160. If the currentIBB, IBB_(C), is less than or equal to the first IBB thresholdIBB_(N)+dIBB₁, and greater than or equal to the second IBB thresholdIBB_(N)−dIBB₂, fault detector 140 is configured to determine that thepotential fault is not detected in positioning device 160.

In some embodiments, the nominal IBB in method 200 includes at least oneof a predetermined value of IBB stored in the at least one memory, aninitialized value of IBB obtained from an initialization of a receiverof the positioning device, or a low-pass filtered value of IBB.

For example, controller 142 of fault detector 140 is configured to reada predetermined value of IBB stored in memory 144 as the nominal IBB,IBB_(N). The predetermined value of IBB may be input and stored inmemory 144 by a user. Alternatively, the predetermined value of IBB maybe an average IBB determined based on signals previously received byreceiver 120 for positioning.

As another example, controller 142 of fault detector 140 may beconfigured to obtain an initialized value of IBB as the nominal IBB,IBB_(N), when receiver 120 is configured to execute an initializationprocedure. When receiver 120 executes the initialization procedure,receiver 120 is configured to estimate an IBB between signals on twofrequency bands of a positioning system. Controller 142 is configured tostore the initialized value of IBB as the nominal IBB, IBB_(N), inmemory 144. Alternatively, controller 142 may be configured to store theinitialized value of IBB as the nominal IBB, IBB_(N), in aone-time-programmable memory.

Alternatively, controller 142 of fault detector 140 can be configured toobtain a low-pass filtered value of IBB as the nominal IBB, IBB_(N).When receiver 120 estimates a plurality of values of IBB between twofrequency bands of a positioning system over a period of time,controller 142 can be configured to low-pass filter the plurality ofvalues of IBB to obtain the low-pass filtered value of IBB as thenominal IBB, IBB_(N). For example, controller 142 may calculate arunning average of the plurality of values of IBB. Controller 142 isconfigured to store the low-pass filtered value of IBB in memory 144.

In some embodiments, the IBB estimation in method 200 includes aplurality of IBB-band estimations corresponding to a plurality of pairsof frequency bands. The first IBB threshold used in method 200 includesa plurality of first IBB-band thresholds corresponding to the pairs offrequency bands. The second IBB threshold used in method 200 includes aplurality of second IBB-band thresholds corresponding to the pairs offrequency bands. Comparing the IBB estimation with the first IBBthreshold in method 200 includes comparing the plurality of IBB-bandestimations with the first IBB-band thresholds, respectively; anddetermining that the IBB estimation is greater than the first IBBthreshold when a number of comparison results that the IBB-bandestimations are greater than the first IBB-band thresholds is greaterthan a first band-number threshold. Comparing the IBB estimation withthe second IBB threshold in method 200 includes comparing the IBB-bandestimations with the second IBB-band thresholds, respectively; anddetermining that the IBB estimation is less than the second IBBthreshold when a number of comparison results that the IBB-bandestimations are less than the second IBB-band thresholds is greater thana second band-number threshold.

For example, positioning device 160 is configured to estimate aplurality of IBB-band estimations corresponding to a plurality of pairsof frequency bands of the GPS system. Fault detector 140 is configuredto obtain the plurality of IBB-band estimations corresponding to theplurality of pairs of frequency bands of the GPS system. The pluralityof IBB-band estimations are, for example, a plurality of currentIBB-band estimations IBB_(Ci) of signals on GPS L1 and L2 frequencybands, i=0, 1, 2, . . . , BP−1, where BP is a total number of the pairsof the frequency bands. One of the pairs of the frequency bands mayinclude the same or different frequency bands as another one of thepairs of the frequency bands. The plurality of current IBB-bandestimations IBB_(Ci), i=0, 1, 2, . . . , BP−1, are collectively definedas an IBB estimation estimated by positioning device 160.

Positioning device 160 obtains a plurality of nominal IBB-bandestimations IBB_(Ni), i=0, 1, 2, . . . , BP−1, after positioning device160 is initialized and starts to receive signals on the pairs of the GPSfrequency bands. The plurality of nominal IBB-band estimations IBB_(Ni)are IBBs between signals of the plurality of pairs of GPS frequencybands when all components of positioning device 160 operate without afault. The nominal IBB-band estimations IBB_(Ni) can be average IBBswhen positioning device 160 operates and provides accurate positionfixes.

Fault detector 140 is configured to obtain from memory 144 a pluralityof first IBB-band thresholds equal to the nominal IBB-band estimationsIBB_(Ni) plus a plurality of first delta values of IBB-band dIBB_(1i),respectively, i.e., the first IBB-band threshold for the pair offrequency bands=IBB_(Ni)+dIBB_(1i), i=0, 1, 2, . . . , BP−1. Theplurality of first delta values of IBB-band dIBB_(1i) can respectivelybe, for example, 2 or 3 centimetres per pair (cm/pair) of frequencybands, which are a plurality of first margins to allow variations inIBBs in the plurality of pairs of frequency bands because of variedgroup delays. The plurality of first IBB-band thresholds are upperlimits of IBB between signals of two frequency bands in each pair offrequency bands, respectively. The plurality of first IBB-bandthresholds IBB_(Ni)+dIBB_(1i), i=0, 1, 2, . . . , BP−1, are collectivelydefined as a first IBB threshold.

Fault detector 140 is also configured to obtain from memory 144 aplurality of second IBB-band thresholds equal to the nominal IBB-bandestimations IBB_(Ni) minus a plurality of second delta values ofIBB-band dIBB_(2i), respectively, i.e., the second IBB-bandthresholds=IBB_(Ni)−dIBB_(2i), i=0, 1, 2, . . . , BP−1. The plurality ofsecond delta values of IBB-band dIBB_(2i) can respectively be, forexample, 2 or 3 centimetres per pair (cm/pair) of frequency bands, whichare a plurality of second margins to allow variations in IBBs in theplurality of pairs of frequency bands because of varied group delays.The plurality of second IBB-band thresholds are lower limits of IBBbetween signals of two frequency bands in each pair of frequency bands,respectively. The plurality of second IBB-band thresholdsIBB_(Ni)−dIBB_(2i), i=0, 1, 2, . . . , BP−1, are collectively defined asa second IBB threshold. The plurality of first IBB-band thresholds,i.e., the upper limits of IBB, are respectively greater than theplurality of second IBB-band thresholds, i.e., the lower limits of IBB.

Determining whether the potential fault is detected at step 240 includesdetermining:

$\begin{matrix}{{{Potential}\mspace{14mu}{Fault}} = \left\{ \begin{matrix}{Detected} & {{{if}\mspace{14mu}{IBB}_{Ci}} > {{IBB}_{Ni} + {{dIBB}_{1i}\mspace{14mu}{for}\mspace{14mu}{BN}\; 1\mspace{14mu}{pairs}}}} \\{Detected} & {{{if}\mspace{14mu}{IBB}_{Ci}} < {{IBB}_{Ni} - {{dIBB}_{2i}\mspace{14mu}{for}\mspace{14mu}{BN}\; 2\mspace{14mu}{pairs}}}}\end{matrix} \right.} & (6)\end{matrix}$

If neither BN1 pairs nor BN2 pairs are achieved in accordance with theabove conditions, determining whether the potential fault is detected atstep 240 includes determining that the potential fault is not detected,where BN1 and BN2 are first and second band-number thresholds.

Specifically, determining whether the potential fault is detected instep 240 includes comparing the current IBB-band estimations IBB_(Ci)with the first IBB-band thresholds IBB_(Ni)+dIBB_(1i), respectively. Inresponse to a number of comparison results that the IBB-band estimationsare greater than the first IBB-band thresholds is greater than or equalto a first band-number threshold BN1, i.e., IBB_(C), >IBB_(Ni)+dIBB_(1i)for BN1 or more pairs, step 240 further includes determining that an IBBestimation is greater than a first ISB threshold.

In response to the number of comparison results that the IBB-bandestimations are greater than the first IBB-band thresholds is less thanthe first band-number threshold BN1, step 240 further includesdetermining that the IBB estimation is less than the first IBBthreshold.

In response to the number of comparison results that the IBB-bandestimations are greater than the first IBB-band thresholds is less thanthe first band-number threshold BN1, step 240 includes comparing thecurrent IBB-band estimations IBB_(Ci) with the second ISB-bandthresholds IBB_(Ni)−dIBB_(2i). In response to a number of comparisonresults that the IBB-band estimations are less than the second ISB-bandthresholds is greater than or equal to a second band-number thresholdBN2, i.e., IBB_(Ci)<IBB_(Ni)−dIBB_(2i) for BN2 or more pairs, step 240further includes determining that the IBB estimation is less than asecond IBB threshold.

In response to the number of comparison results that the IBB-bandestimations are less than the second ISB-band thresholds is less thanthe second band-number threshold BN2, step 240 further includesdetermining that the IBB estimation is greater than the second IBBthreshold.

In some embodiments, in step 240, either the comparisons between thecurrent IBB-band estimations and the first ISB-band thresholds or thecomparisons between the current IBB-band estimations and the secondIBB-band thresholds may be performed before the other. When either ofthe comparisons are performed, the other of the comparisons may not beperformed. Alternatively, when either of the comparisons are performed,the other of the comparisons may still be performed.

Moreover, step 240 further includes determining that the potential faultis detected in response to at least one of: a determination that the IBBestimation is greater than the first IBB threshold, or a determinationthat the IBB estimation is less than the second IBB threshold.

In other words, if the number of comparison results that the IBB-bandestimations are greater than the first IBB-band thresholds is greaterthan or equal to the first band-number threshold BN1, i.e.,IBB_(Ci)>IBB_(Ni)+dIBB_(1i) for BN1 or more pairs, fault detector 140 isconfigured to determine that a potential fault is detected inpositioning device 160. If the number of comparison results that theIBB-band estimations are less than the second ISB-band thresholds isgreater than or equal to the second band-number threshold BN2, i.e.,IBB_(Ci)<IBB_(Ni)−dIBB_(2i) for BN2 or more pairs, fault detector 140 isconfigured to determine that a potential fault is detected inpositioning device 160.

In some embodiments, fault detector 140 can be configured to compare theIBB-band estimations with the first or second ISB-band thresholds untilBN1 or BN2 pairs are achieved as described in equation (6) and determinethat a potential fault is detected in positioning device 160. Faultdetector 140 may be configured not to compare the remaining IBB-bandestimations with the remaining first or second IBB-band thresholds.

In some embodiments, fault detector 140 is configured to compare theIBB-band estimations with one or more of the first IBB-band thresholdsand one or more of the second IBB-band thresholds until a thirdband-number threshold BN3 is achieved. If a sum of (a) a first number ofcomparison results that the IBB-band estimations are greater than thefirst IBB-band thresholds and (b) a second number of comparison resultsthat the IBB-band estimations are less than the second IBB-bandthresholds, is greater than or equal to the third band-number thresholdBN3, fault detector 140 is configured to determine that a potentialfault is detected in positioning device 160.

In some embodiments, the nominal IBB-band estimations in method 200include at least one of predetermined values of IBB-band stored in theat least one memory, initialized values of IBB-band obtained from aninitialization of the positioning device, or low-pass filtered values ofIBB-band, similar to the nominal IBB described above with reference toequation (5).

In some embodiments, the information in step 220 includes a gain controlparameter and a bias estimation. The detection threshold in step 240includes a gain threshold, a first bias threshold, and a second biasthreshold. The first bias threshold is greater than the second biasthreshold. Determining whether the potential fault is detected in step240 includes comparing the gain control parameter with the gainthreshold; at least one of: comparing the bias estimation with the firstbias threshold, or comparing the bias estimation with the second biasthreshold; and determining that the potential fault is detected inresponse to: a comparison result that the gain control parameter isgreater than the gain threshold, and one of (i) a comparison result thatthe bias estimation is greater than the first bias threshold, or (ii) acomparison result that the bias estimation is less than the second biasthreshold.

For example, fault detector 140 is configured to obtain informationabout a current gain G_(c) of PGA 360 and a current ICB, ICB_(C),between two GLONASS FDMA channels, as described with reference toequations (1) and (2) and FIGS. 1-3. Fault detector 140 is configured toobtain from memory 144 a gain threshold equal to the nominal gain G_(N)plus a delta value of gain dG, i.e., the gain threshold=G_(N)+dG. Faultdetector 140 is also configured to obtain from memory 144 a first ICBthreshold equal to the nominal ICB, ICB_(N), plus the first delta valuedICB₁, i.e., the first ICB threshold=ICB_(N)+dICB₁, and a second ICBthreshold equal to the nominal ICB, ICB_(N), minus the second deltavalue dICB₂, i.e., the second ICB threshold=ICB_(N)−dICB₂, as describedwith reference to equations (1) and (2) and FIGS. 1-3. The first ICBthreshold, i.e., the upper limit of ICB, is greater than the second ICBthreshold, i.e., the lower limit of ICB.

Fault detector 140 is configured to compare the current gain G_(c) ofPGA 360 with the gain threshold G_(N)+dG. Fault detector 140 is alsoconfigured to compare the current ICB, ICB_(C), with the first ICBthreshold ICB_(N)+dICB₁, and/or compare the current ICB, ICB_(C), withthe second ICB threshold ICB_(N)−dICB₂. Fault detector 140 is configuredto determine that the potential fault is detected in response to: acomparison result that the current gain G_(c) of PGA 360 is greater thanthe gain threshold G_(N)+dG and one of (i) a comparison result that thecurrent ICB, ICB_(C), is greater than the first ICB thresholdICB_(N)+dICB₁, or (ii) a comparison result that the current ICB,ICB_(C), is less than the second ICB threshold ICB_(N)−dICB₂.

In some embodiments, fault detector 140 can be configured to obtaininformation about one or more of a current gain G_(c), of PGA 360, acurrent ICB, ICB_(C), between two channels, a current ISB_(C) betweensignals of two GNSS constellations, and/or a current IBB_(C) betweensignals on two frequency bands, as described above with references toequations (1)-(6) and FIGS. 1-5. Fault detector 140 can be configured todetermine that the potential fault is detected in response to two ormore of those conditions in equations (1)-(6) are met.

In some embodiments, information in step 220 includes an estimation ofat least one of an input spectrum to the positioning device, or aresulting residual of pseudorange measurements for a given estimatedposition with estimated biases applied based on the received signal.

For example, fault detector 140 is configured to obtain an estimation ofan input spectrum to positioning device 160. The input spectrum includesa standard deviation of samples of an ADC of positioning device 160. AGC122 is configured to control the gain of PGA 360 to maintain thestandard deviation of the samples of the ADC constant, which supports adynamic range of receiver 120. When all components of positioning device160 operate without a fault, AGC 122 can control the gain of PGA 360 tomaintain the standard deviation of the samples of the ADC substantiallyconstant.

When a fault exists in one of the components of positioning device 160,the fault may cause an anomalous standard deviation among samples of theADC. The anomalous standard deviation among samples of the ADC may begreater than a standard deviation threshold because of the fault in theone of the components of positioning device 160. Accordingly, method 200can be practiced by fault detector 140 for detecting a potential faultin one of the components of positioning device 160 based on the standarddeviation of samples of the ADC and the standard deviation threshold,similar to steps described above for fault detection based on the gainof PGA 360 and the gain threshold and equation (1). Alternatively, faultdetector 140 can be configured to detect a potential fault based on thestandard deviation among samples of the ADC, the gain of PGA 360, thestandard deviation threshold, and the gain threshold. The latteralternative may provide a shorter reaction time of fault detection.

As another example, fault detector 140 can be configured to obtain aresulting residual of pseudorange measurements for a given estimatedposition with estimated biases applied based on a received signal. Whenpositioning device 160 is configured to estimate for a given position,each measurement may include a resulting residual of pseudorangemeasurement because of noise and/or interference. When all components ofpositioning device 160 operate without a fault, the residual ofpseudorange measurement is expected to increase or decrease linearlyover different frequencies, i.e., different channels.

When a fault exists in one of the components of positioning device 160,the fault may cause an anomalous increase in an absolute value of theresidual of pseudorange measurement. Before receiver 120 adjusts an ICBestimation to minimize the residual of pseudorange measurement, theabsolute value of the anomalous residual of pseudorange measurement maybe greater than a residual threshold because of the fault in the one ofthe components of positioning device 160. Accordingly, method 200 can bepracticed by fault detector 140 for detecting a potential fault in oneof the components of positioning device 160 based on the resultingresidual of pseudorange measurement and the residual threshold, similarto steps described above for fault detection based on the gain of PGA360 and the gain threshold and equation (1).

Another aspect of the disclosure is directed to a non-transitoryprocessor-readable medium storing instructions which, when executed,cause one or more processors to perform the methods discussed above. Theprocessor-readable medium may include volatile or non-volatile,magnetic, semiconductor, tape, optical, removable, non-removable, orother types of processor-readable medium or processor-readable storagedevices. For example, the processor-readable medium may be the storagedevice or the memory module having the processor instructions storedthereon, as disclosed. In some embodiments, the processor-readablemedium may be a disc or a flash drive having the processor instructionsstored thereon.

It will be appreciated that the present disclosure is not limited to theexact construction that has been described above and illustrated in theaccompanying drawings, and that various modifications and changes can bemade without departing from the scope thereof. It is intended that thescope of the application should only be limited by the appended claims.

What is claimed is:
 1. An apparatus for detecting a potential fault in apositioning device, the apparatus comprising: at least one memory forstoring instructions; and at least one controller configured to executethe instructions to perform operations comprising: obtaining informationabout a received signal received by the positioning device, theinformation comprising at least one of a control parameter or anestimation of bias based on the received signal; determining whether thepotential fault is detected, based on the information and a detectionthreshold; and responsive to a determination that the potential fault isdetected, generating an indication that the potential fault is detected.2. The apparatus of claim 1, wherein: the information comprises a gaincontrol parameter; the detection threshold comprises a gain threshold;and determining whether the potential fault is detected comprises:comparing the gain control parameter with the gain threshold; andresponsive to a comparison result that the gain control parameter isgreater than the gain threshold, determining that the potential fault isdetected.
 3. The apparatus of claim 2, wherein: the gain controlparameter comprises a current gain of a programmable gain amplifier(PGA) in a receiver of the positioning device; and the gain thresholdcomprises a nominal gain of the PGA plus a delta value of gain.
 4. Theapparatus of claim 3, wherein the nominal gain comprises at least oneof: a predetermined value of gain stored in the at least one memory, aninitialized value of gain obtained from an initialization of thereceiver, or a low-pass filtered value of gain.
 5. The apparatus ofclaim 1, wherein: the information comprises an inter-channel bias (ICB)estimation between two channels of a positioning system; the detectionthreshold comprises a first ICB threshold and a second ICB threshold,wherein the first ICB threshold is greater than the second ICBthreshold; and determining whether the potential fault is detectedcomprises: at least one of: comparing the ICB estimation with the firstICB threshold; or comparing the ICB estimation with the second ICBthreshold; and determining that the potential fault is detectedresponsive to one of: a comparison result that the ICB estimation isgreater than the first ICB threshold; or a comparison result that theICB estimation is less than the second ICB threshold.
 6. The apparatusof claim 5, wherein: the ICB estimation comprises a current ICBestimation; the first ICB threshold comprises a nominal ICB estimationplus a first delta value of ICB; and the second ICB threshold comprisesthe nominal ICB estimation minus a second delta value of ICB.
 7. Theapparatus of claim 6, wherein the nominal ICB estimation comprises atleast one of: a predetermined value of ICB stored in the at least onememory, an initialized value of ICB obtained from an initialization of areceiver of the positioning device, or a low-pass filtered value of ICB.8. The apparatus of claim 5, wherein the ICB estimation comprises anestimation of group delay between the two channels of the positioningsystem.
 9. The apparatus of claim 1, wherein: the received signal is afirst received signal from a first positioning system; the positioningdevice is configured to receive a second received signal from a secondpositioning system; the information comprises an inter-system bias (ISB)estimation between the first and second positioning systems based on thefirst and second received signals; the detection threshold comprises afirst ISB threshold and a second ISB threshold, wherein the first ISBthreshold is greater than the second ISB threshold; and determiningwhether the potential fault is detected comprises: at least one of:comparing the ISB estimation with the first ISB threshold; or comparingthe ISB estimation with the second ISB threshold; and determining thatthe potential fault is detected responsive to one of: a comparisonresult that the ISB estimation is greater than the first ISB threshold;or a comparison result that the ISB estimation is less than the secondISB threshold.
 10. The apparatus of claim 9, wherein: the ISB estimationcomprises a current ISB estimation; the first ISB threshold comprises anominal ISB estimation plus a first delta value of ISB; and the secondISB threshold comprises the nominal ISB estimation minus a second deltavalue of ISB.
 11. The apparatus of claim 10, wherein the nominal ISBestimation comprises at least one of: a predetermined value of ISBstored in the at least one memory, an initialized value of ISB obtainedfrom an initialization of a receiver of the positioning device, or alow-pass filtered value of ISB.
 12. The apparatus of claim 9, wherein:the ISB estimation is a first ISB estimation; the positioning device isconfigured to receive a third received signal from a third positioningsystem; the information further comprises a second ISB estimationbetween the first and third positioning systems based on the first andthird received signals; the detection threshold further comprises athird ISB threshold and a fourth ISB threshold, wherein the third ISBthreshold is greater than the fourth ISB threshold; and determiningwhether the potential fault is detected further comprises: at least oneof: comparing the second ISB estimation with the third ISB threshold; orcomparing the second ISB estimation with the fourth ISB threshold; anddetermining that the potential fault is detected responsive to one of: acomparison result that the second ISB estimation is greater than thethird ISB threshold; or a comparison result that the second ISBestimation is less than the fourth ISB threshold.
 13. The apparatus ofclaim 1, wherein: the information comprises an inter-band bias (IBB)estimation between two frequency bands of the positioning system; thedetection threshold comprises a first IBB threshold and a second IBBthreshold, wherein the first IBB threshold is greater than the secondIBB threshold; and determining whether the potential fault is detectedcomprises: at least one of: comparing the IBB estimation with the firstIBB threshold; or comparing the IBB estimation with the second IBBthreshold; and determining that the potential fault is detected,responsive to one of: a comparison result that the IBB estimation isgreater than the first IBB threshold; or a comparison result that theIBB estimation is less than the second IBB threshold.
 14. The apparatusof claim 13, wherein: the IBB estimation comprises a current IBBestimation; the first IBB threshold comprises a nominal IBB estimationplus a first delta value of IBB; and the second IBB threshold comprisesthe nominal IBB estimation minus a second delta value of IBB.
 15. Theapparatus of claim 13, wherein the nominal IBB estimation comprises atleast one of: a predetermined value of IBB stored in the at least onememory, an initialized value of IBB obtained from an initialization of areceiver of the positioning device, or a low-pass filtered value of IBB.16. The apparatus of claim 13, wherein: the IBB estimation comprises aplurality of IBB-band estimations corresponding to a plurality of pairsof frequency bands; the first IBB threshold comprises a plurality offirst IBB-band thresholds corresponding to the pairs of frequency bands;the second IBB threshold comprises a plurality of second IBB-bandthresholds corresponding to the pairs of frequency bands; comparing theIBB estimation with the first IBB threshold comprises: comparing theplurality of IBB-band estimations with the first IBB-band thresholds,respectively; and determining that the IBB estimation is greater thanthe first IBB threshold when a number of comparison results that theIBB-band estimations are greater than the first IBB-band thresholds isgreater than a first band-number threshold; and comparing the IBBestimation with the second IBB threshold comprises: comparing theIBB-band estimations with the second IBB-band thresholds, respectively;and determining that the IBB estimation is less than the second IBBthreshold when a number of comparison results that the IBB-bandestimations are less than the second IBB-band thresholds is greater thana second band-number threshold.
 17. The apparatus of claim 1, wherein:the information comprises a gain control parameter and a biasestimation; the detection threshold comprises a gain threshold, a firstbias threshold, and a second bias threshold, wherein the first biasthreshold is greater than the second bias threshold; and determiningwhether the potential fault is detected comprises: comparing the gaincontrol parameter with the gain threshold; at least one of: comparingthe bias estimation with the first bias threshold; or comparing the biasestimation with the second bias threshold; and determining that thepotential fault is detected responsive to: a comparison result that thegain control parameter is greater than the gain threshold; and one of(i) a comparison result that the bias estimation is greater than thefirst bias threshold; or (ii) a comparison result that the biasestimation is less than the second bias threshold.
 18. The apparatus ofclaim 1, wherein the information comprises an estimation of at least oneof: an input spectrum to the positioning device, or a resulting residualof pseudorange measurements for a given estimated position withestimated biases applied based on the received signal.
 19. A method fordetecting a potential fault in a positioning device, the methodcomprising: obtaining information about a received signal received bythe positioning device, the information comprising at least one of acontrol parameter or an estimation of bias based on the received signalin the positioning device; determining whether the potential fault isdetected, based on the information and a detection threshold; andresponsive to a determination that the potential fault is detected,generating an indication that the potential fault is detected.
 20. Anon-transitory computer-readable medium for storing instructions which,when executed, cause a controller to perform operations for detecting apotential fault in a positioning device, the operations comprising:obtaining information about a received signal received by thepositioning device, the information comprising at least one of a controlparameter or an estimation of bias based on the received signal;determining whether the potential fault is detected, based on theinformation and a detection threshold; and responsive to a determinationthat the potential fault is detected, generating an indication that thepotential fault is detected.